Modulated molecular beam growth of mixed As/Sb layers for mid-infrared lasers

Short period superlattices of the ternary InGaAs/InGaSb alloys are grown by molecular beam epitaxy with the intent of approximating a quaternary InGaAsSb alloy. This technique where a quaternary semiconductor alloy is replaced by building short period superlattices using its ternary constituents is referred to as 'digital alloying.' Three sets of 2 micrometer In0.1Ga0.9AsySb1-y bulk alloys are grown; the first set was grown conventionally with varying growth temperature, while the other two sets were grown digitally. The first set of digital alloys lattice matched to GaSb is grown at various substrate temperatures, the second set was grown at one constant growth temperature but with various superlattice periodicities. Using high-resolution x-ray diffraction and room temperature photoluminescence, the structural and optical properties of the bulk In0.1Ga0.9AsySb1-y alloys were investigated. It is observed that the digital alloys are less sensitive to changes in the growth temperature by a factor of approximately 3, and the maximum periodicity a digital alloy can be grown before the onset of relaxation is approximately 9 ML. An optically pumped approximately 2 micrometer laser structure with InGaAsSb quantum wells and AlGaAsSb barriers both grown using the digital alloy technique was characterized. Room temperature operation, a low threshold current density of 104 W/cm2 (at 80 K with 808 nm pump), and a high characteristic temperature (TO) of 104 K show the feasibility of applying digital alloying techniques to mid-infrared optical devices.